This invention relates to the extraction of oil from oil sand. In particular it relates to an improvement whereby a higher proportion of the oil is recovered and less goes into the effluent. The term "oil" as used herein is intended to be used in its generic sense and would include bitumen and tar.
A method has been described for recovering oil from oil sand in which the oil sand is tumbled in an aqueous alkaline solution to form a floating mass which contains oil. The floating mass can be froth or a slurry. In most cases there are at least two frothing or flotation tanks where typically the slurry or foam is fed into a first tank at about 180.degree. F. and the sand and clay allowed to settle. The mixture of oil sand and aqueous alkali which forms on the top of the solution is a froth, emulsion or flotation fed to a second tank for further tumbling and settling. In the second stage more water is generally added and the temperature generally increased to about 200.degree. F. U.S. Pat. Nos. 3,330,757 and 3,893,907 are patents which deal with this general method. Most of the sand and clay is drained off the bottom of the tanks and the emulsion, slurry, froth or flotation, which contains the oil, is then skimmed off the top and passed into a naphtha solution for dissolving the oil. The naphtha step is typically followed by centrifuging to remove any sand or clay that may have carried over. The effluent line typically draws commonly both from the tanks and the centrifuge. The naphtha is separated from the oil by distillation.
One problem with this method is that some of the oil does not go into the froth or floatation and thus ends up in the effluent lines with consequent pollution of the down stream.
One object of the present invention is to provide an improvement on this method which will increase the amount of oil going into the froth or flotation and decrease the amount of oil going into the effluent.
Other objects and advantages of this invention will be apparent from the description and claims which follow.